Optic flow and sea-land orientation in the sandhopper Talitrus saltator.

The problem sandhoppers face when they find themselves on the dry sand is to reach as quickly as possible the belt of moist sand near the water. In the present study, I ask whether, alongside many other orienting factors, sandhoppers use the optic flow they experience to maintain their bearing relative to the sea-land axis. Adult individuals of Talitrus saltator were released in a transparent Plexiglas bowl, horizontally placed between four walls with a pattern of vertical black and white stripes. The orientation of one pair of opposite walls was south-north, orthogonal to the sea-land axis of the home beach, whilst the second pair of walls was oriented east-west. The black and white striped pattern of opposite walls could be moved in pairs and in the same direction (speed=4.8 cm s(-1)). The results demonstrate that the optic flow sandhoppers experience when moving on the sea-land axis of their home beach influences their direction of travel and could help sandhoppers in maintaining a straight path to reach favourable ground by the shortest route.